Anaerobic co-digestion of linen, sugar beet pulp, and wheat straw with cow manure: effects of mixing ratio and transient change of co-substrate

Abstract

This study concerns the improvement and sustainability of producing methane (CH4) from the co-digestion of cow manure (CM), sugar beet pulp (SBP), linen (Ln), and wheat straw (WS). The first step involved co-digesting CM, Ln, and WS at various mixing ratios (CM/Ln/WS) in batch reactors to ascertain the best gas production. Biochemical methane potential (BMP) tests were carried out under mesophilic conditions using sludge from a wastewater treatment plant as an inoculum. The highest CH4 production (351 mL/g VSadd) and volatile solids removal rate (72.87%) were observed at the mixing ratio 50/25/25 and the lowest CH4 production (187 mL/g VSadd) was recorded at the ratio 25/25/50. A kinetic analysis was carried out to suggest the best strategy for methane production based on the ratio of substrates in the mix. The second step involved co-digesting CM, SBP, Ln, and WS in a semi-continuous stirred tank reactor to study the influence of a transient change in co-substrate on gas production and reactor performance. The rate of biogas production doubled with the transient change of co-substrate from WS to SBP, which may be due to the SBP being more easily biodegradable than WS.

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Biomass Conversion and Biorefinery
https://doi.org/10.1007/s13399-021-02229-8
ORIGINAL ARTICLE
Anaerobic co‑digestion oflinen, sugar beet pulp, andwheat straw
withcow manure: effects ofmixing ratio andtransient change
ofco‑substrate
MahmoudElsayed1 · YvesAndres3· WalidBlel2
Received: 18 July 2021 / Revised: 10 December 2021 / Accepted: 13 December 2021
© The Author(s) 2022
Abstract
This study concerns the improvement and sustainability of producing methane (CH4) from the co-digestion of cow manure
(CM), sugar beet pulp (SBP), linen (Ln), and wheat straw (WS). The first step involved co-digesting CM, Ln, and WS at
various mixing ratios (CM/Ln/WS) in batch reactors to ascertain the best gas production. Biochemical methane potential
(BMP) tests were carried out under mesophilic conditions using sludge from a wastewater treatment plant as an inoculum.
The highest CH4 production (351mL/g VSadd) and volatile solids removal rate (72.87%) were observed at the mixing ratio
50/25/25 and the lowest CH4 production (187mL/g VSadd) was recorded at the ratio 25/25/50. A kinetic analysis was carried
out to suggest the best strategy for methane production based on the ratio of substrates in the mix. The second step involved
co-digesting CM, SBP, Ln, and WS in a semi-continuous stirred tank reactor to study the influence of a transient change in
co-substrate on gas production and reactor performance. The rate of biogas production doubled with the transient change of
co-substrate from WS to SBP, which may be due to the SBP being more easily biodegradable than WS.
Keywords Cow manure· Linen· Wheat straw· Sugar beet pulp· Mixing ratio· Transient change of co-substrate
1 Introduction
It is a major goal for many European Union (EU) nations
to increase their production of green energy from renew-
able resources. The production of energy from biogas, in
the form of electricity, has developed significantly in the EU
as a result of its environmental and economic advantages
[17]. Over the last few decades, a huge quantity of animal
manure has been disposed of by traditional methods, which
represents a main source of air and water pollution [20].
Anaerobic digestion (AD), where a combination of bac-
teria convert the organic waste to methane (CH4) and other
gases [9], is an effective treatment for manure. However,
digesting manure alone results in low biogas production [6],
and several authors have tested the anaerobic co-digestion
of manure with other waste materials, such as agricultural
waste, to enhance production (Liu, Jinming, Changhao
Zeng, Na Wang, Jianfei Shi, Bo Zhang, Changyu Liu, 2021).
Improvements in carbon to nitrogen (C/N) ratio, feedstock
nutrient balance and gas production have been observed as
a result of mixing the nitrogen-rich manure with the high
carbon content of agricultural waste [12].
Of all agricultural waste materials, sugar beet pulp (SBP)
appears to be a suitable substrate for AD due to its high car-
bohydrate content [28]. Total SBP production in the EU was
207.93 million tonnes in 2018 [15]. Wheat straw is another
widely available crop worldwide, with 771.71 million tonnes
produced in 2017 [14].
Crop residues from sugar beet pulp, linen (Ln) and wheat
straw (WS) are some of the best co-substrates to mix with
animal manure for improved CH4 production and alkalinity,
and increased bacterial activity (Elsayed etal., 2017; Yang
etal., 2021).
Manure has been digested alone and in co-digestion with
SBP in previous studies, but the improvement in CH4 pro-
duction by adding Ln and WS to the co-digestion of manure
* Mahmoud Elsayed
m.elsayed@aswu.edu.eg
1 Civil Engineering Department, Faculty ofEngineering,
Aswan University, Aswan81542, Egypt
2 Oniris, Université de Nantes, GEPEA, CNRS UMR 6144,
44600Saint-Nazaire, France
3 IMT Atlantique, GEPEA, UMR CNRS 6144, Cedex 3, 4 Rue
Alfred Kastler, 44307Nantes, France
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Biomass Conversion and Biorefinery
1 3
and SBP, and study of the effects of transient co-substrate
changes using different waste materials (in multi-substrates)
is poorly documented. Fonoll etal. [16] showed that replac-
ing the co-substrate with a similar feedstock did not result
in system failure. Fanget al. [13] reported that using SBP as
a co-substrate improved CH4 production from the anaerobic
digestion of manure. Elsayed etal. [8] reported that CH4
production from the anaerobic co-digestion of sludge and
straw was improved by adding buckwheat husk at a C/N
ratio of 10. Borowski and Kucner [6] showed that increasing
the manure by content by 20% can improve CH4 production
from the anaerobic co-digestion of SBP and sludge at an
organic loading rate of 4.25kg VS/m3.d. Babaee etal. [4]
studied the co-digestion of manure and WS,they reported
that CH4 production was increased by 43% at a tempera-
ture of 35°C. Aboudi etal. [1] studied the semi-continuous
digestion of sugar beet by-product with manure, the result
showed that the optimal CH4 production was conducted at
an organic load of 11.2kg VS/m3.d.
As a first step in this study, the production of CH4 from
anaerobic digestion of CM in a batch reactor was improved
by adding WS and Ln at different mixing ratios. In terms
of sustainability, it is important to use the residues of dif-
ferent crops to avoid suspending the biogas production in
the reactor when a certain crop is out of season; this will be
of enormous benefit to the industry. In a second step, since
the effects of transient co-substrate changes using different
waste materials have been poorly documented in previous
works, this study also investigated the effects of a transient
change in the co-substrate in multi-substrates on gas pro-
duction and reactor performance, using a semi-continuous
stirred tank reactor.
2 Methodology
2.1 Preparation ofsubstrates
Cow manure (CM) was acquired from a small farm in
Coueron (GAEC des Marais, France), homogenized and
stored at -3°C for later use. SBP, WS and Ln were obtained
from a farm in Nantes (France) and ground with a Retsch
SM 300 cutting mill (Germany) to reduce particle size to
below 1.0mm for optimum CH4 production, as recom-
mended by Yong etal. [27].
2.2 Inoculum
For this work, the inoculum was used from the IMT Atlan-
tique reactor (GEPEA laboratory, Nantes, France). The
sludge was obtained from the Saint-Nazaire (France) waste-
water treatment plant, comprising 60% digested sludge and
40% activated sludge. The original temperature of the inocu-
lum in the reactor was 37°C.
2.3 Analytical techniques
A Flash EA 1112 (Thermo Finnigan, IMT Atlantique,
France) was used to analyze the elements (C, N, H, O) in this
study. The volatile solids, total solids, and pH were analyzed
using APHA Standard Methods [3]. The biogas production
rate was analyzed by the water displacement method, using
an Agilent Innovations G2801A (China). The cumulative
biogas production was assessed to STP values (105Pa and
273.15K). The characteristics of the substrate and inoculum
are shown in Table1.
Table 1 Characterization of
feedstock and inoculum
Notes: VS volatile solids, TS total solids, TC total carbon, TN total nitrogen, TO total oxygen, TH total
hydrogen, C/N nitrogen to carbon ratio. The data represent the mean ± SD, n = 3
Characteristics CM SBP Ln WS Inoculum
VS (TS %) 65.91 ± 0.13 96.22 ± 0.13 98.20 ± 0.10 94.23 ± 0.12 81.97 ± 0.08
TS (dry wt. %) 6.79 ± 0.12 85.00 ± 0.36 88.42 ± 0.15 88.33 ± 0.18 4.123 ± 0.36
TC (dry wt. %) 38.81 ± 0.32 41.17 ± 0.30 48.64 ± 0.44 46.50 ± 0.58 ND
TN (dry wt. %) 2.80 ± 0.16 2.4 ± 0.12 0.59 ± 0.25 0.33 ± 0.04 ND
TO (dry wt. %) 30.20 ± 0.15 46.11 ± 0.02 28.30 ± 0.19 42.35 ± 0.42 ND
TH (dry wt. %) 6.10 ± 0.12 6.54 ± 0,34 5.98 ± 0.09 6.14 ± 0.17 ND
pH 8.50 ± 0.15 ND ND ND 7.08 ± 0.09
C/N ratio 13.86 17.15 82.44 140.91 ND
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Biomass Conversion and Biorefinery
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2.4 Experiment design andset‑up
3 Biochemical methane potential (BMP) test
The biochemical methane potential (BMP) test was car-
ried out first, in triplicate, using 500mL bottles and under
mesophilic conditions, based on the method described
by Elsayed etal. [8]. The anaerobic co-digestion of CM,
Ln and WS was carried out using various mixing ratios
of 100/00/00, 70/15/15, 50/25/25, 34/33/33, 25/50/25,
25/25/50, 00/100/00, and 00/00/100 respectively, to obtain
the best mixing ratio for high gas production (Table2).
4 Semi‑continuous reactor
The semi-continuous co-digestion of CM, Ln and WS or
SBP was carried out using a stainless steel semi-continuous
stirred tank reactor (SSTR-MP30) (Fig.1). The total volume
of the SSTR was 75 L and the maximum available working
volume 50 L. The temperature of the SSTR was controlled
using a coolant-circulating jacket to ensure mesophilic con-
ditions for the bacterial activity (37 ± 1°C). The reactor had
a light-up window for viewing the processed substrate inside
the tank. The substrate was fed into the reactor by two peri-
staltic pumps and mixing in the reactor was controlled using
a marine propeller agitator.
To monitor the effects of the transient co-substrate change
on anaerobic co-digestion (using the optimal mixing ratio
obtained in the BMP test), three runs were carried out. For
run 0, the SSTR reactor was loaded with inoculum alone for
10days, to activate micro-organisms under mesophilic condi-
tions [18]. In run 1, semi-continuous co-digestion of CM, Ln
and WS was carried out with a 35 L working volume and an
organic loading rate (OLR) of 1 kgVS/m3. d (37° C ± 1). In run
2, semi-continuous co-digestion of CM, Ln and SBP was car-
ried out, replacing the WS co-substrate with SBP, to examine
the effects that changing the co-substrate had on the biogas
production rate and biodegradability of the substrates used
in multi-substrates (Table3). The hydraulic retention time of
Table 2 Anaerobic co-digestion
in batch reactor of CM, Ln and
WS at different mixing ratios
CM cow manure, Ln linen, WS wheat straw
Batch reactor
number
CM (gVS/400mL) Ln (gVS/400mL) WS gVS/400mL) Mixing ratio
(CM/Ln/
WS)
T1 5.25 1.13 1.13 70/15/15
T2 3.75 1.88 1.88 50/25/25
T3 2.55 2.48 2.48 34/33/33
T4 1.88 3.75 1.88 25/50/25
T5 1.88 1.88 3.75 25/25/50
C1 7.5 0.00 0.00 100/00/00
C2 0.00 7.5 0.00 00/100/00
C3 0.00 0.00 7.5 00/00/100
Fig. 1 Batch reactor test set-up
[8]
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Biomass Conversion and Biorefinery
1 3
15days was kept constant for the two steps, feeding the reac-
tor with 2.33 L of feedstock (substrates + water) and removing
2.33 L from the reactor each day.
In expansion, approximately 100mL of the digestate was
established every 3days before feeding the reactor, to assess
the biodegradability of the substrates. The CH4 content was
analyzed twice a week for the amount of biogas produced
(Fig.2).
4.1 Kinetic analysis ofcumulative biogas
production
The modified Gompertz equation (Eq.1) proposed by [22]
is used to describe the kinetics of methane production. This
model has been used by several authors where the biogas pro-
duction has a lag phase, enabling prediction of the adaptation
phase prior to methane production, when the substrate presents
a high concentration of the less-biodegradable compounds [10,
11, 19].
(1)
H
(t)=P.exp
[
−exp
[
Rm.e
P(𝜆−t)+1
]]
where H (t) is the accumulative methane production (mL/
gvsadd), P the methane production potential (mL/g VSadd),
Rm the maximum methane production rate (mL/g VSadd/
day), λ the lag-phase time (days) and e = 2.718281828.
4.2 Statistical analysis
For this study, statistical analysis was carried out using
ANOVA analysis, the tested conditions were compared
using STAT GRA PHICS Centurion XV software (Virginia,
USA), and the differences in biogas production with vari-
ous fractions of CM, Ln and WS were analyzed at a con-
fidence interval of 95%.
Table 3 Characteristics of
transient co-substrate change in
semi-continuous co-digestion of
CM, Ln and WS or SBP
Notes: CM cow manure, Ln linen, WS wheat straw, SBP sugar beet pulp, OLR organic loading rate, HRT
hydraulic retention time
Run CM (kgVS) Ln (kgVS) WS (kgVS) SBP (kgVS) OLR
(kgVS/
m3. d)
HRT (days) Mixing ratio
Run 0 0.00 0.00 0.00 0.00 0.0 10 0.00
Run 1 122.5 61.25 61.25 0.00 1.0 15 50:25:25
Run 2 122.5 61.25 0.00 61.25 1.0 15 50:25:25
Fig. 2 MP30 Methanization
reactor
0
5
10
15
20
25
30
35
40
45
50
12345678910111213141516171819202122232425262728293
0
)ddaSVg/Lm(noitcudorpenahtemyliaD
Time (Day)
100/00/00
70/15/15
50/25/25
34/33/33
25/50/25
25/25/50
00/100/00
00/00/100
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Biomass Conversion and Biorefinery
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5 Results anddiscussion
5.1 Anaerobic co‑digestion ofCM, Ln andWS
inabatch reactor
6 CH4 production
Daily CH4 yields from the co-digestion of CM, Ln and WS
at different mixing ratios using the batch reactor are shown
in Fig.3. The peak values at mixing ratios of 100/00/00,
70/15/15, 50/25/25, 34/33/33, 25/50/25, 25/25/50, 00/100/00
and 00/00/100 were 19.8, 45, 39.2, 27.8, 19.5, 24.7, 20 and
23mL/g VSadd, respectively, obtained mainly between the
day 11 and day 15 of AD. The highest peak was recorded at
the mixing ratio of 70/15/15 on day 12 from the start of the
BMP test, while the lowest value was recorded at the mixing
ratio of 25/50/25 on day 14. This may be because the mixing
ratio of 70/15/15 contained a high percentage of CM and
lower percentages of Ln and WS; these agricultural wastes
contain cellulose and other non-digestible matter, which it is
not easily degraded by micro-organisms [10, 11, 23].
The cumulative methane yields (CMYs) from co-diges-
tion of CM, Ln and WS at normal temperature and pressure
(N) conditions are shown in Fig.4. The CMYs from co-
digestion at mixing ratios 100/00/00, 70/15/15, 50/25/25,
Fig. 3 Daily CH4 production
from co-digestion of CM, Ln,
and WS
0
50
100
150
200
250
300
350
12345678910 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
30
)ddaSVg/Lm(sdleiyenahtemevitalumuC
Time (Day)
100/00/00
70/15/15
50/25/25
34/33/33
25/50/25
25/25/50
00/100/00
00/00/100
Fig. 4 CMYs from co-digestion
of CM, Ln and WS
46
48
50
52
54
56
58
60
51015202
53
0
Methane content (%)
Time (Day)
100/00/0070/15/15 50/25/25
34/33/33 25/50/25 25/25/50
00/100/00 00/00/100
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Biomass Conversion and Biorefinery
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34/33/33, 25/50/25, 25/25/50, 00/100/00 and 00/00/100
were 180, 326, 351, 240, 205, 187, 153 and 211mL/g VSadd,
respectively. The CMYs observed with the various mixing
ratios were higher than those for individual digestion of the
feedstock used. An analysis of variance (ANOVA) test on
the cumulative methane yields (CMYs) for co-digestion tests
showed a P-value for the F-test of less than 0.05, with a sta-
tistically significant difference between the mean cumulative
methane from one CM/Ln/WS mixing ratio to another at
a confidence level of 95%. A comparison of mixing ratios
showed that CMYs were higher with an increase in CM
percentage. The mixing ratio of 50/25/25 is statistically the
optimum for high methane production. This mixing ratio
contains a low percentage of hemi-cellulose and lignin.
Hemi-cellulose and lignin are not easily biodegradable [25]
due to the stability of cellulose microfibers and the poly-
saccharidic coating [2]. However, the lowest CMYs were
observed at the mixing ratios 25/25/50 and 25/50/25.
7 CH4 content andVS removal rate
The methane (CH4) content from co-digestions of CM, Ln,
and WS is shown in Fig.5. The highest average CH4 per-
centages were observed at the mixing ratios 70/15/15 and
50/25/25, while the lowest value was at the ratio 25/50/25.
However, the CH4 percentages for the various mixes were
higher than those obtained from individual digestion of the
feedstock used. A comparison of the various mixing ratios
shows that the CH4 content was higher when the CM per-
centage in the ratio was increased.
The VS removal rates and pH values for co-digestion of
CM, Ln and WS are shown in Fig.6. The VS removal rates
increased more gradually at the mixing ratios 50/25/25 and
70/15/15 than at the other ratios. The lowest VS removal rate
was recorded at the mixing ratio 25/50/25. Finally, the pH
values ranged between 7.11 and 7.52, which is considered an
acceptable range for micro-organism growth [21].
8 Kinetic analysis ofcumulative biogas
production atdierent CM/Ln/WS ratios
Figure7 represents the estimated and observed CMYs
from anaerobic co-digestion of CM, Ln and WS at differ-
ent mixing ratios. The curves were estimated using Eq.1,
which predicts two-phase anaerobic digestion: an initial
phase of biogas production from the easily-biodegradable
material, and a second phase of degradation of the material
after it has been subjected to a biological hydrolysis step,
and with a time lag λ between the two phases [10, 11]. As
a first observation, this model provides a good description
of the AD of the various mixes,the presence of an agri-
cultural substrate in the mix explains the inflection point
corresponding to the lag phase prior to biogas production.
The parameters of the modified Gompertz equation are
set out in Table4. The low RMSE values show that the
CMYs observed are closely aligned with the theoretical
values. Table4 also shows the lag times of between 4 and
5days observed for the various mixes tested, demonstrat-
ing that this parameter depends more on the nature of the
substrates than on their percentage in the mix. In cases
using other types of substrates, such as activated sludge,
longer lag times of around 15days have been observed
[10, 11], confirming this result. It is also observed that
maximum biogas productivity is obtained for the 50/25/25
mix, with an estimated CMY value of 378.6mL/g VSadd
and a maximum methane production rate (Rm) of 20.02ml
/gVSadd/day. The model also provides for higher biogas
production when the CM concentration is higher; the low
kinetic parameters were obtained under conditions where
the CM concentration was zero. Given the high nitrogen
concentration in the CM (Table1), this result shows the
effects of this substrate in the C/N mixing ratio, producing
the most favourable conditions for optimal microbiologi-
cal activity.
Fig. 5 Average CH4 content
from co-digestions of CM, Ln,
and WS
6.9
7
7.1
7.2
7.3
7.4
7.5
7.6
1
11
21
31
41
51
61
71
81
100/00/0070/15/1550/25/2534/33/3325/50/2525/25/5000/100/00 00/00/100
VS removal rate (%)
Mixing ratios
VS pH
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8.1 Semi continuous co‑digestion ofCM, SBP, Ln,
andWS
9 Eects oftransient change ofco‑substrate
formulti‑digestion
The effects of a transient change in co-substrate for multi-
digestion using different waste materials are shown in Fig.8.
In this part, three runs were conducted. In the initial step
(run 0), the lowest daily biogas yield was observed when
the SSTR reactor was fed with inoculum only. In run 1,
the semi-continuous co-digestion of CM, Ln and WS was
Fig. 6 VS removal rates and pH
values from co-digestions of
CM, Ln and WS
0
50
100
150
200
250
300
350
400
0510 15 20 25 30
g/Lm(sdleiysagoibevitalumuC
ddaSV
)
Time (day)
100/00/00
70/15/15
50/25/25
34/33/33
25/50/25
25/25/50
00/100/00
00/00/100
Nonlinear estimation results
according to Eq.1
Fig. 7 Estimated and observed
CMYs from anaerobic co-
digestion of CM, Ln and WS
at different mixing ratios (CM/
Ln/WS)
Table 4 Kinetic parameters of BMP tests calculated from non-linear
regression of Eq.1
Mixing ratio
(CM/Ln/WS)
P (ml/gVSadd) Rm (ml/
gVSadd/
day)
Lamda (Day) RMSE
100/00/00 184.35 10.72 4.72 2.452
70/15/15 336.13 20.20 5.16 4.834
50/25/25 378.62 20.02 4.92 4.715
34/33/33 257.71 13.33 4.19 3.206
25/50/25 220.40 11.14 4.59 2.352
25/25/50 201.22 10.27 4.28 3.005
00/100/00 161.83 8.48 4.78 2.383
00/00/100 228.95 11.65 4.33 2.681
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carried out using the organic loading rate (OLR) of 1 kgVS/
m3. d. In this stage, the daily biogas yields increased more
gradually than in the initial step, as a result of feeding the
reactor with CM, Ln and WS. The highest daily biogas
yields from co-digestion of CM, Ln and WS were 5.93 and
5.81 L/d, observed on days 18 and 14 respectively. In run 2,
the co-substrate WS was replaced with SBP to examine the
effects of changing the co-substrate (in multi-substrates) on
biogas yields and biodegradability. In this stage, the daily
biogas yields increased more gradually than in run 1 (where
WS was used as co-substrate). The highest daily biogas
yields from co-digestion of CM, Ln and SBP were 17.06 and
16.13 L/d, recorded on days 34 and 33 respectively, a yield
2.88 and 2.78 times higher than the highest values observed
in run 1 (biogas yields two times higher than the values
recorded in run 1). In general, a transient change of co-sub-
strate using different waste materials and multi-substrates
improves biogas yields and increases the sustainability of
gas production throughout the year, since harvesting seasons
demand that different types of crop are used. For this study,
we started the semi-continuous co-digestion of CM and Ln
with the abundant crop WS; for the second step, we replaced
WS with SBP, also considered an abundant crop, to study
the effects of a transient change of co-substrate on biogas
production. However, WS was the only substrate replaced
with SBP, in order to maintain the stability of the reactor.
Finally, it is important to use the residues of different
crops in season to avoid suspending biogas production in
the reactor. This will be of enormous benefit to the industry.
This result coincides with previous studies: Fonoll etal. [16]
studied the effects of substituting different types of fruit with
sludge for gas production, compared with mono-digestion
of the fruits. The results showed that changing one kind of
fruit with the same type did not cause system failure. In
this study, however, we examined the effects of a transient
change of co-substrate (for multi-substrates) on biogas pro-
duction and system stability.
The VS removal rate and methane (CH4) content for the
transient change of co-substrate are shown in Fig.8. CH4
content increased slightly with a change in co-substrate from
WS (in run 1) to SBP (in run 2). The highest CH4 content
of 54.33% (day 24) and 57.54% (day 33) were observed in
runs 1 and 2 respectively. In addition, the VS removal rate
increased gradually when the co-substrate was changed from
WS (Run 1) to SBP (Run 2). The maximum VS removal
rates of 68.14% and 68.64% were achieved in runs 1 and
2 respectively. The results show that a transient change of
co-substrate from WS to SBP has a positive effect on VS
removal rate and CH4 content, improving them both.
10 Conclusion
This work reports on the sustainability of improving CH4
production from the co-digestion of CM, SBP, Ln and WS
based on their mixing ratios and a transient change of co-
substrate. A BMP test was first carried out to ascertain the
mixing ratio for highest gas production from the co-digestion
of CM, WS and Ln. The results show first of all the best
CH4 production at a mixing ratio of 50/25/25, with a value
of 351mL/g VSadd. However, VS removal rates and CH4
content were shown to gradually increase at mixing ratios of
50/25/25 and 70/15/15 compared to the other ratios. These
results are confirmed by the kinetic study. In the subsequent
experiments, the semi-continuous co-digestion of CM, SBP,
Ln, and WS was carried out to study the effects of transient
change in operating parameters on gas production and reac-
tor performance. The advantages of this study are the sus-
tainability of CH4 production in the off-season, which will
be a great advantage for the industry. The results show that
a transient change of co-substrate in multi-substrates could
double the daily CH4 production when the co-substrate is
changed from WS to SBP, and that CH4 production is there-
fore sustainable.
Fig. 8 Daily biogas yields for
semi-continuous co-digestion of
CM, Ln and SBP (or WS)
0
10
20
30
40
50
60
70
80
12 15 18 21 24 27 30 33 36 39
etarlavomerSVdna)%(stnetnocenahteM
Time (Day)
CH4%
VS removal
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Acknowledgements This work was supported by GEPEA UMR CNRS
6144 (IMT Atlantique, France) and Aswan University (Egypt).
Funding Open access funding provided by The Science, Technology &
Innovation Funding Authority (STDF) in cooperation with The Egyp-
tian Knowledge Bank (EKB).
Open Access This article is licensed under a Creative Commons Attri-
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